1. Field of the Invention
The present invention relates to an image forming apparatus configured to select a full-color operating mode for producing a full-color image and a monochrome operating mode for producing a monochrome image (i.e., black and white image), and more particularly to an image forming apparatus configured to adjust phases of image carriers after conducting an image forming operation in the full-color or monochrome operating modes.
2. Description of the Related Art
Image forming apparatuses having a full-color operating mode for transferring color or black toner images from image carriers to a transfer member, and a monochrome operating mode for transferring black toner images from an image carrier to a transfer member have been publicly known and marketed as, for example, electro-photocopying apparatuses, printers, and facsimiles or as multi-functional apparatuses having at least one combination of these devices. The transfer member in these apparatuses may include an intermediate transfer member, and a recording medium, onto which images are recorded and fixed.
In order to prevent color displacement in a full-color image formed on the transfer member (i.e., intermediate transfer member or recording medium) in the above-mentioned image forming apparatus, a predetermined phase relationship is required between the color and black image carriers. One way of setting the phase relationship between the image carriers is to adjust eccentricity positions of each of the image carriers. Hereinafter, in order to simplify the description, the color and black image carriers are collectively referred as “image carriers.”
During monochrome image formation operation, the color image carriers are disengaged from the transfer member, and only the black image carrier rotates to form a black toner image on the transfer member. Therefore, after a monochrome image forming operation, the predetermined phase relationship, which is set for the color and black image carriers for full-color operation, may deviate from an original setting.
Accordingly, after completion of a monochrome image forming operation, an operation to align the phases between the color and black image carriers is conventionally conducted by adjusting a stop position of the black image carrier. Such phase alignment operation can also be conducted after completion of a full-color image forming operation.
During image forming operations on a full-color or monochrome operating modes, the image carriers are rotated in one direction for forming toner images and transferring the toner images to the transfer member and, after completion of the image forming operation, the image carriers are stopped. However, image carriers may be configured to rotate in the opposite direction (i.e., opposite to the direction of rotation during image forming) after the image forming operation. When the direction of rotation is changed, deposits (e.g., toners and paper powders) accumulated on an edge of a cleaning blade may be dropped, thus permitting the cleaning blade to be effectively cleaned.
In such conventional arrangement, if the image carriers rotate in the inverse direction after conducting the above-mentioned phase alignment operation, the predetermined phase relationship between the full-color and black image carriers may deviate from an optimal position, resulting in a color displacement of the full-color image produced in the next image forming operation.